With the rapid growth of wireless mobile communication markets, various multimedia services are required in a wireless environment. To provide the multimedia services, researches are conducted on a multi-antenna (Multiple Input Multiple Output (MIMO)) system to efficiently utilize limited frequencies in response to mass data transmission and fast data transmission.
The multi-antenna system can increase a transmission reliability and a data rate, compared to a single-antenna system, by sending data over independent channels for the respective antennas without additional frequencies or transmit power allocation. For example, the multi-antenna system can enhance system performance through a diversity scheme and increase the data rate through a spatial multiplexing scheme.
When the spatial multiplexing scheme is used in the multi-antenna system, a transmitting end can increase the data rate by transmitting different data based on streams over transmitting antennas. A receiving end can reduce a gain by interference between the data received through the streams.
Hence, in the case of little interference between the streams, the multi-antenna system can increase a capacity gain using the spatial multiplexing scheme. However, in the case of considerable interference between the streams, the spatial multiplexing scheme may decrease the capacity gain due to the data interference. Accordingly, in the great interference between the streams, the multi-antenna system can acquire a stable link using the diversity scheme.
As discussed above, using the diversity scheme and the spatial multiplexing scheme, the multi-antenna system attains the gain which differs based on the channel environment. Therefore, the multi-antenna system demands a technique for selectively using the transmission mode based on the channel environment.